Such magnetic field sensors are suited for the measurement of magnetic fields the strength of which are only a few nT to mT for example as a compass for measuring the direction of the earth's magnetic field.
A magnetic field sensor of the type named in the preamble of claim 1 is known from EP 1 052 519 A1 as well as from the article “CMOS planar 2D micro-fluxgate sensor” by the authors L. Chiesi, P. Kejik, B. Janossy and R. S. Popovic, which was published in the magazine Sensors and Actuators 82 (2000) 174–180. Such a magnetic field sensor contains a ferromagnetic core and an excitation coil through which alternating current flows in order to alternately magnetically saturate and demagnetise the core. An important disadvantage of this sensor exists in that an adequate sensitivity has to be taken at the expense of a relatively large ferromagnetic core. This stands in the way of a further miniaturisation and makes the sensor relatively expensive. A further problem exists in that the ferromagnetic core can be unintentionally magnetised by an outer magnetic field that is much larger than the actual field to be measured. The current flowing in the coil is then no longer able to freely align the individual magnetic domains, which leads to a measuring error.
A device for measuring one single component of a magnetic field is known from EP 359 922 A1 with which a ring-shaped ferromagnetic core serves to chop the magnetic field the direction of which is fixed. The ferromagnetic core however does not serve as a flux concentrator.